Polycarbonate resin (hereinafter may be referred to as “PC”) having advantages such as heat resistance, impact resistance, and transparency, has been employed in various fields such as exterior materials, electronic and electric uses, and optical disk substrates. Polycarbonate resins having such advantages have further been applied to uses such as automobiles and medical materials. As applications expand, improvement of resistance to chemicals has been keenly demanded.
In order to improve resistance of PC to chemicals, there has been carried out melt mixing of a saturated polyester resin serving as a modifier into PC. For example, use of polyethylene terephthalate (hereinafter may be referred to as “PET”) as a modifier for PC has been proposed. However, addition of PET is known to considerably impair transparency of PC. In order to solve this problem, measures currently undertaken include use of a method of melt mixing employing a long residence time and a method of melt mixing employing a Ti-base catalyst. However, even when these measures are taken, obtained transparency is not sufficient, and there arise problems of yellowing of the composition caused by thermal decomposition, and generation of gases such as aldehyde during decomposition. In addition, since PET has a relatively low glass transition temperature (Tg), heat resistance of the resin composition becomes very low, which is also problematic.
When polybutylene terephthalate resin (hereinafter may be referred to as “PBT”) is employed as a modifier for PC, a certain level of transparency is attained. However, the transparency is not yet satisfactory, and heat resistance decreases considerably, which is also problematic. Meanwhile, there has been proposed a thermoplastic resin composition including PC and a modified PET, in which diol units are changed to 1,4-cyclohexanedimethanol units (40 mol %) (Japanese Patent Application Laid-Open (kokai) No. 2000-63641). However, the resin composition has a drawback of reduced heat resistance and poor resistance to chemicals, although the resin composition has good transparency.
There has also been proposed use, as a modifier for PC, of a copolymer polyester containing a predetermined proportion of naphthalenedicarboxylic acid units in the dicarboxylic acid units of the resin (Japanese Patent Application Laid-Open (kokai) No. 2000-103948). However, when naphthalenedicarboxylic acid units are incorporated into the dicarboxylic acid units in a proportion required for improving resistance to chemicals, transparency problematically decreases to an unsatisfactory level. Thus, hitherto, there has never been known a PC-polyester resin-based composition which maintains transparency and heat resistance of PC and which has improved resistance to chemicals.
Meanwhile, as compared with PCs, polyester resins such as PET, polyethylene naphthalate, and PBT are generally excellent in resistance to chemicals, moldability, printability, etc. but are poor in heat resistance, mechanical strength (particularly impact strength), and transparency. Thus, improvement of such poor physical properties is demanded.
For the purpose of improving properties of a polyester resin, such as heat resistance and impact strength, a thermoplastic resin produced by adding PC to the polyester through melt mixing has been proposed. However, as mentioned above, the thus-produced polyester resin has considerably poor transparency. Thus, hitherto, there has never been known a thermoplastic composition which has both improved heat resistance and improved mechanical strength (particularly impact strength) of polyester resin as well as high transparency.
As mentioned above, there has never been known a thermoplastic resin composition which is formed of a polycarbonate resin and a polyester resin and which has excellent transparency, heat resistance, resistance to chemicals, and mechanical strength (particularly impact strength) as well as moldability, printability, etc.